Photoelectric converter, focus detection apparatus, and optical apparatus which are used for autofocusing

ABSTRACT

A photoelectric converter includes a photoelectric conversion portion (PD) which receives light from an object to generate charges, a transfer portion (MTX) which transfers the charges generated by the photoelectric conversion portion, a capacitance portion (Cfd, Cs) which accumulates the charges transferred from the transfer portion, a determination unit ( 109 ) which determines whether an accumulation of the charges in the capacitance portion is to be stopped based on a signal corresponding to a charge amount accumulated in the capacitance portion during a first time period, and a setting unit (ST) which sets a height of a potential barrier in the transfer portion (transfer channel region), and the setting unit changes the height of the potential barrier in the transfer portion between the first time period and a second time period different from the first time period.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a photoelectric converter which is usedfor autofocusing by a phase-difference detection method.

Description of the Related Art

Japanese Patent Laid-open No. 2013-54333 discloses a focus detectionsensor which has a first accumulation mode and a second accumulationmode. In the first accumulation mode, the focus detection sensorintegrates charges generated by a photoelectric conversion element in apixel without transferring the charges to a memory unit until completionof a charge accumulation period, and it transfers the charges after thecompletion of the charge accumulation period. In the second accumulationmode, the focus detection sensor transfers the charges generated by thephotoelectric conversion element during the charge accumulation periodto the memory unit, and it monitors an integrated value of the chargesin the memory unit.

However, when the focus detection sensor disclosed in Japanese PatentLaid-open No. 2013-54333 is used with a high dynamic range in the secondaccumulation mode, the linearity is deteriorated.

SUMMARY OF THE INVENTION

The present invention provides a photoelectric converter, a focusdetection apparatus, and an optical apparatus which improve linearitywith a high dynamic range.

A photoelectric converter as one aspect of the present inventionincludes a photoelectric conversion portion configured to receive lightfrom an object to generate charges, a transfer portion configured totransfer the charges generated by the photoelectric conversion portion,a capacitance portion configured to accumulate the charges transferredfrom the transfer portion, a determination unit configured to determinewhether an accumulation of the charges in the capacitance portion is tobe stopped based on a signal corresponding to a charge amountaccumulated in the capacitance portion during a first time period, and asetting unit configured to set a height of a potential barrier in thetransfer portion, and the setting unit is configured to change theheight of the potential barrier in the transfer portion between thefirst time period and a second time period different from the first timeperiod.

A photoelectric converter as another aspect of the present inventionincludes a photoelectric conversion portion configured to receive lightfrom an object to generate charges, a transfer portion configured totransfer the charges generated by the photoelectric conversion portion,a capacitance portion configured to accumulate the charges transferredfrom the transfer portion, and a determination unit configured todetermine, based on a detection signal corresponding to a charge amountaccumulated in the capacitance portion, whether an accumulation of thecharges in the capacitance portion is to be stopped, the detectionsignal being obtained while the transfer portion transfers the charges,and the determination unit is configured to determine whether theaccumulation of the charges in the capacitance portion is to be stopped,by using information relating to a difference between a first signalcorresponding to an accumulation amount accumulated in the capacitanceportion while the transfer portion stops transferring the charges and asecond signal corresponding to an accumulation amount accumulated in thecapacitance portion while the transfer portion transfers the changes.

A focus detection apparatus as another aspect of the present inventionincludes the photoelectric converter and a detection unit configured todetect a defocus amount based on the signal.

An optical apparatus as another aspect of the present invention includesthe focus detection apparatus and a lens drive unit configured to drivea lens based on the defocus amount detected by the detection unit.

Further features and aspects of the present invention will becomeapparent from the following description of exemplary embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an AF sensor in each embodiment.

FIG. 2 is a block diagram of an image pickup apparatus in eachembodiment.

FIG. 3 is an optical configuration diagram of the image pickup apparatusin each embodiment.

FIG. 4 is an optical configuration diagram of an AF sensor unit in eachembodiment.

FIGS. 5A and 5B are diagrams of illustrating a positional relationshipbetween a line sensor and a focus detection area in each embodiment.

FIG. 6 is a circuit configuration diagram of the line sensor in eachembodiment.

FIG. 7 is a timing chart of illustrating a charge accumulation operationin a second accumulation mode in a first embodiment.

FIGS. 8A and 8B are schematic diagrams of a potential of an AF sensorand generated charges as a comparative example.

FIGS. 9A and 9B are diagrams of illustrating a relationship between anaccumulation time of the charges in the AF sensor and an FD voltage(output voltage) as the comparative example.

FIG. 10 is a schematic diagram of a potential of an AF sensor andgenerated charges in the first embodiment.

FIG. 11 is a flowchart of a focus detection operation in the firstembodiment.

FIG. 12 is a flowchart of illustrating an adjustment operation of anaccumulation stop level in a second embodiment.

FIG. 13 is a diagram of illustrating a change of an FD voltage (outputvoltage) according to ON/OFF of a transfer transistor in the secondembodiment.

FIG. 14 is a flowchart of a focus detection operation in the secondembodiment.

FIG. 15 is a diagram of illustrating a relationship of pixel signalsaccording to ON/OFF of the transfer transistor in the second embodiment.

FIG. 16 is a timing chart of illustrating a charge accumulationoperation in a second accumulation mode in a third embodiment.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described belowwith reference to the accompanied drawings.

First Embodiment

First, referring to FIG. 2, an image pickup apparatus (opticalapparatus) in a first embodiment of the present invention will bedescribed. FIG. 2 is a block diagram of illustrating a configuration ofa main part of an image pickup apparatus 10 (digital camera).

In FIG. 2, a CPU 100 (camera microcomputer) is a control unit(processor) that controls the whole of a camera (image pickup apparatus10). The CPU 100 is connected to a signal input circuit 204 that detectssignals of switches 214 used for various operations of the image pickupapparatus 10, an image sensor 206 (image pickup element, or image pickupunit), and an AE sensor 207. The CPU 100 is connected to a shuttercontrol circuit 208 that controls magnets 218 a and 218 b (shuttermagnets) and an AF sensor 101 (focus detection sensor, or photoelectricconverter). The CPU 100 is capable of transmitting signals 215 from andto an imaging lens 300 (see FIG. 3) via a lens communication circuit205, and it can control a focus position and an aperture stop. Theoperation of the image pickup apparatus 10 is determined according tothe setting of the switches 214.

The AF sensor 101 includes a plurality of line sensors (see FIG. 5A).The CPU 100 includes a control unit (detection unit) that detects adefocus amount based on an image signal (i.e., signal corresponding to acharge amount accumulated in the AF sensor 101) of an object obtainedfrom the line sensors of the AF sensor 101 and that controls a focusposition of the imaging lens 300. Furthermore, the CPU 100 has afunction as a calculation unit that performs focus detection calculationbased on a signal obtained from the line sensor of the AF sensor 101.The AF sensor 101 and the CPU 100 constitute a focus detectionapparatus. The lens communication circuit 205 includes a lens drive unitthat drives the imaging lens 300. The lens drive unit drives a lens(imaging lens 300) based on the defocus amount detected by the detectionunit (CPU 100).

The CPU 100 detects a luminance of an object obtained by the AE sensor207 and determines an aperture value (F number) of the imaging lens 300and a shutter speed. Then, the CPU 100 controls the aperture value viathe lens communication circuit 205. The CPU 100 adjusts an energizingtime of the magnets 218 a and 218 b via the shutter control circuit 208to control the shutter speed. Furthermore, the CPU 100 controls theimage sensor 206 to perform a photographing operation (image capturingoperation).

Next, referring to FIG. 3, an optical configuration of the image pickupapparatus 10 will be described. FIG. 3 is an optical configurationdiagram of the image pickup apparatus 10. Most of light beams from anobject incident via an image pickup optical system including the imaginglens 300 are reflected by a quick return mirror 305 upward, and areimaged as an object image on a finder screen 303. A user of the imagepickup apparatus 10 can view this image via a pentaprism 301 and aneyepiece 302.

Parts of the light beams from the object incident via the imaging lens300 transmit through the quick return mirror 305, and then they are bentdownward by a sub mirror 306 disposed at a back side. The light beamsbent by the sub mirror 306 are imaged on the AF sensor 101 via a fieldmask 307, a field lens 308, an aperture stop 309, and a secondaryimaging lens 310. The AF sensor 101 photoelectrically converts thisimage (optical image) to output an image signal. Then, the CPU 100processes the image signal output from the AF sensor 101, and thus itcan detect a focus state of the imaging lens 300. In photography, thequick return mirror 305 moves upward, and accordingly all the lightbeams from the object incident via the imaging lens 300 are imaged onthe image sensor 206 so that exposure of an object image is performed.In other words, the image sensor 206 photoelectrically converts theobject image (optical image) formed by the image pickup optical systemincluding the imaging lens 300.

In this embodiment, an optical system including the field mask 307, thefield lens 308, the aperture stop 309, and the secondary imaging lens310, and the AF sensor 101 constitute an AF sensor unit. The AF sensorunit performs focus detection by a well-known phase-difference detectionmethod.

Next, referring to FIG. 4, an optical configuration of the AF sensorunit in this embodiment will be described in detail. FIG. 4 is anoptical configuration diagram of an AF sensor unit 20. Light beams froman object passing through the imaging lens 300 are reflected by the submirror 306 (see FIG. 3), and then they are imaged once near the fieldmask 307 disposed on a plane which is conjugate to an imaging plane ofthe image sensor 206. The field mask 307 is a light shielding memberthat shields extra light other than light in a focus detection area in ascreen.

The field lens 308 has a function of imaging each opening of theaperture stop 309 near an exit pupil of the imaging lens 300. Thesecondary imaging lens 310 is disposed behind the aperture stop 309. Thesecondary imaging lens 310 includes a pair of lenses, and the lensescorrespond to the respective openings of the aperture stop 309. Eachlight beam passing through the field mask 307, the field lens 308, theaperture stop 309, and the secondary imaging lens 310 is imaged on theline sensor of the AF sensor 101.

Next, referring to FIGS. 5A and 5B, a positional relationship betweenthe line sensors of the AF sensor 101 and focus detection areas (AFframes) in the screen will be described. FIGS. 5A and 5B are diagrams ofillustrating the positional relationship between the line sensors andthe focus detection areas. FIG. 5A illustrates an arrangement of linesensors 102 to 105 in the AF sensor 101. Each of the line sensors 102 to105 includes a pair of line sensors. Each line sensor includes aplurality of pixels arranged in line, and an image signal is output fromeach pixel. The CPU 100 can detect a focus state (defocus amount) of theimaging lens 300 based on a phase difference of a pair of image signalsobtained from the pair of line sensors. The line sensor is projected onapproximately the same area (predetermined area) on a field of view(screen) by an optical system (focus detection optical system) such asthe secondary imaging lens 310, and a position of this area correspondsto a position of the focus detection area.

FIG. 5B illustrates a positional relationship between the focusdetection areas and the line sensors in a finder screen 500corresponding to the AF sensor 101 illustrated in FIG. 5A. In the finderscreen 500 (field of view), there are a total of three focus detectionareas of a focus detection area 503 corresponding to the line sensor105, a focus detection area 501 corresponding to the line sensors 102and 103, and a focus detection area 502 corresponding to the line sensor104. However, this embodiment is not limited to thereto, and thearrangement and the number of the focus detection areas may bearbitrarily modified.

Next, referring to FIG. 1, the configuration of the AF sensor 101 willbe described in detail. FIG. 1 is a block diagram of illustrating theconfiguration of the AF sensor 101. An object image (optical image)imaged by the secondary imaging lens 310 is photoelectrically convertedby the line sensors 102 to 105 into charges (electric charges) to beaccumulated. The line sensor 102 includes a photodiode PD (photoelectricconversion portion), a transfer transistor MTX (transfer portion), anintegral capacity Cfd (capacitance portion), and a memory capacity Cs(capacitance portion). The line sensors 103 to 105 also have the sameconfiguration as that of the line sensor 102. Details of each elementconstituting the line sensor 102 will be described below.

A controller 106 (control unit) receives an instruction (command) fromthe CPU 100 to control each portion in the AF sensor 101, and itcontrols an accumulation of the charges or a readout operation in eachof the line sensors 102 to 105. Furthermore, the controller 106 sends,to the CPU 100, information of the line sensor for which it isdetermined that the accumulation is to be stopped. The CPU 100 includesa memory 1061 (memory unit) that stores predetermined information.

A line selection circuit 107 selects any one of the line sensors 102 to105. Then, the line selection circuit 107 outputs pixel signals of theselected line sensor to a signal amount detection circuit 108 and anoutput circuit 111. The signal amount detection circuit 108 detects amaximum signal (peak signal) of the pixel signals of the line sensorselected by the line selection circuit 107. Then, the signal amountdetection circuit 108 outputs the detected peak signal to the CPU 100via an accumulation stop determination circuit 109 and the outputcircuit 111. The accumulation stop determination circuit 109 comparesthe peak signal with an accumulation stop level (predetermined thresholdvalue, or reference value) to determine whether the accumulation of thecharges is to be stopped (i.e., perform an accumulation stopdetermination of the charges). The accumulation stop level is adjustableas appropriate, and it can be set to an arbitrary level (referencevalue) via communication from the CPU 100.

When the peak signal is larger than the accumulation stop level, theaccumulation stop determination circuit 109 outputs an accumulation stopdetermination signal to the controller 106. When the controller 106receives the accumulation stop determination signal, it outputs acontrol signal to the line sensor which is subject to the accumulationstop determination so as to stop the accumulation operation of the linesensor. Furthermore, the controller 106 outputs, to the CPU 100, anaccumulation completion signal and information of the line sensor wherethe accumulation is terminated. On the other hand, when the peak signaldoes not reach a target value (predetermined threshold value) within apredetermined time, the CPU 100 can also output an accumulation stoprequest signal to the controller 106 so as to stop the accumulation ofthe charges forcibly. While the accumulation stop determination isperformed based on the peak signal in this embodiment, the accumulationstop determination may be performed based on a feature amount such as acontrast of the image signals obtained from the line sensor.

When an output request of the pixel signals of the line sensor isreceived from the CPU 100, the controller 106 controls the lineselection circuit 107 to select the targeted line sensor. Then, thecontroller 106 outputs a control signal to a shift register 110 tocontrol the shift register 110 so as to output the pixel signals frompixels of the line sensor one by one to the output circuit 111. Theoutput circuit 111 performs various kinds of processing such asamplification processing on the pixel signals, and it outputs theprocessed signals to an A/D converter (not illustrated) of the CPU 100.

Next, referring to FIG. 6, a circuit of the line sensor 102 will bedescribed in detail. FIG. 6 is a circuit configuration diagram of theline sensor 102. Each of the line sensors 103 to 105 have the samecircuit configuration as that of the line sensor 102, and accordinglydescriptions thereof are omitted.

The line sensor 102 includes a photodiode PD, an integral capacity Cdfas a capacity of a floating diffusion region (FD region), a transfertransistor MTX, and a memory capacity Cs. Furthermore, the line sensor102 includes a current source 1, a current source 2, a MOS transistorsM1, M2, M3, M4, and M5, and switches SWRES, SWCH, and LSEL.

The photodiode PD is a photoelectric conversion element. Chargesgenerated by the photodiode PD are transferred to the FD region via thetransfer transistor MTX. In this embodiment, the transfer transistor MTXis a PMOS. A control signal φTXn (n=1 to 4) is an ON/OFF signal of thetransfer transistor MTX, and it is applied to a gate of the transfertransistor MTX via an inverter circuit INV. Symbols VTXL and VTXHindicate voltages that are supplied from a power source of the invertercircuit INV, and they are used as a gate voltage of the transfertransistor MTX. The inverter circuit INV and the power source thatsupplies the voltages VTXL and VTXH constitute a setting unit ST(setter). As described below, the setting unit ST sets a height of apotential barrier of a transfer channel region in the transfertransistor MTX. When the gate of the transfer transistor MTX is to beturned on, the voltage VTXL is applied to the gate according to thecontrol signal φTXn, and accordingly charges generated by the photodiodePD are transferred to the FD region.

On the other hand, when the gate of the transfer transistor MTX is to beturned off, the voltage VTXH is applied to the gate according to thecontrol signal φTXn. In this case, the charges generated by thephotodiode PD are integrated in the photodiode PD without beingtransferred to the FD region. Symbol n (=1 to 4) corresponds to therespective line sensors 102 to 105, and the controller 106 can control atransfer timing of the charges for each line sensor by controlling thecontrol signal φTXn independently.

A voltage VRES is a reset voltage for resetting the photodiode PD andthe integral capacity Cfd to be in an initial state, and it is suppliedfrom a power source (not illustrated). The switch SWRES is a resetswitch, and it is turned on or off according to a control signal φRES.The MOS transistors M1 to M5, the current source 1, and the currentsource 2 constitute a signal buffer amplifier. The charges transferredto the FD region are converted into a voltage (voltage signal) by theintegral capacity Cfd. This voltage signal is output to the followingstage via the signal buffer amplifier. By turning off the switch SWCHthat is coupled to the memory capacity Cs disposed at an output side ofthe signal buffer amplifier, the voltage signal can be stored in thememory capacity Cs.

The switch SWCH is turned on or off according to a control signal φCHn(n=1 to 4). Symbol n (=1 to 4) corresponds to the respective linesensors 102 to 105. The controller 106 can control a timing for storingthe voltage signal in the memory capacity Cs for each line sensor bycontrolling the control signal φCHn independently. In this embodiment,by turning off the switch SWCH, the voltage signal is stored in thememory capacity Cs. The switch LSEL is a switch used for connecting thevoltage signal during accumulation of charges and the voltage signalstored in memory capacity Cs to the line selection circuit 107 disposedat the following stage. The switch LSEL is turned on or off according toa line selection signal φLSn (n=1 to 4). Symbol n (=1 to 4) correspondsto the respective line sensors 102 to 105.

The AF sensor 101 of this embodiment has a first accumulation mode(first mode) and a second accumulation mode (second mode) as disclosedin Japanese Patent Laid-open No. 2013-54333. In other words, in thefirst accumulation mode, the AF sensor 101 integrates the chargesgenerated by the photodiode PD (photoelectric conversion element) in apixel without transferring the charges to the memory capacity Cs (memoryunit) until completion of a charge accumulation period, and it transfersthe charges to the memory capacity Cs (memory unit) after the completionof the charge accumulation period. In the second accumulation mode, theAF sensor 101 transfers the charges generated by the photodiode PD(photoelectric conversion element) during the charge accumulation periodto the memory capacity Cs (memory unit), and it monitors an integratedvalue of the charges in the memory unit. The charge accumulation periodis a time period during which the photodiode PD receives light forperforming focus detection (acquiring signals for the focus detection)using the AF sensor 101.

Referring to FIGS. 8A, 8B, 9A, and 9B, the deterioration of thelinearity which occurs when the AF sensor 101 is used with a highdynamic range in the second accumulation mode will be described. FIGS.8A and 8B are schematic diagrams of a potential of each portion andcharges in a state where the transfer transistor MTX is turned on duringaccumulation of the charges in the second accumulation mode and thecharges accumulated in the photodiode PD are being transferred to thefloating diffusion region (FD region). The potential of each portioncorresponds to a height of a potential (potential barrier). A potential(height of the potential barrier) of the transfer transistor MTX(transfer channel region) can be controlled by the voltages VTXL andVTXH (gate voltage), and it is set to be lower than a potential of thephotodiode PD. FIG. 8A illustrates a state in which the voltageVTXL=VTXL1 is applied (set) as a gate voltage of the transfer transistorMTX (i.e., a first state in which the height of the potential barrier isa first height PB1). FIG. 8B illustrates a state in which the voltageVTXL=VTXL2 that is higher than the voltage VTXL1 is applied (set) as agate voltage of the transfer transistor MTX (i.e., a second state inwhich the height of the potential barrier is a second height PB2 that ishigher than the first height PB1).

FIGS. 9A and 9B correspond to FIGS. 8A and 8B, respectively, and theyare diagrams of illustrating a relationship between an accumulation timeand an FD potential (output voltage) in a situation where constant lightis illuminated on the photodiode PD. As illustrated in FIG. 9A, in theconfiguration of FIG. 8A, the FD potential increases with apredetermined inclination from a start of the accumulation of charges,and the linearity is deteriorated after a time T1 passes. This isbecause the FD potential becomes higher than a potential of the transfertransistor MTX, and as a result charges in the FD region gets into underthe gate of the transfer transistor MTX to result in an increase of anapparent FD capacity.

In order to solve the problem, the potential of the transfer transistorMTX is controlled to be set to the voltage VTXL=VTXL2 so as to becomehigher than the voltage of the case in FIG. 8A, and as a result, thecharges in the FD region cannot easily get into under the gate of thetransfer transistor MTX as illustrated in FIG. 8B. In this case,however, a time (transfer time) required for completely transferring thecharges generated by the photodiode PD to the FD region increases.Accordingly, as illustrated in FIG. 9B, a degree (inclination) of therise of the FD potential is small until a time T2. Typically, when anobject is dark and the number of generated charges is small, thetransfer time tends to increase.

The AF sensor 101 of this embodiment reduces the deterioration of thelinearity even when it is used with a high dynamic range in the secondaccumulation mode. FIG. 7 is a timing chart of illustrating a chargeaccumulation operation of the second accumulation mode in thisembodiment. In this embodiment, the gate potential in the ON state ofthe transfer transistor MTX is set to the voltage VTXL=VTXL1 to becontrolled.

In FIG. 7, a time period from times t0 to t1 is a pixel reset timeperiod. When the communication for starting the accumulation is sentfrom the CPU 100, the controller 106 of the AF sensor 101 turns on theswitch SWRES and the transfer transistor MTX to reset each of potentialsof the photodiode PD and the integral capacity Cfd to the voltage VRESaccording to the control signals φRES and φTXn. The transfer transistorMTX keeps the ON state after the time t1, and accordingly the chargesgenerated by the photodiode PD are accumulated in the integral capacityCfd.

During a time period from times t2 to t3, the line selection switchesLSEL of the line sensor 102 to 105 are turned on in sequence accordingto line selection signals φLSn. Signals of the line sensor selected bythe line selection switch LSEL are output to the signal amount detectioncircuit 108. Then, the signal amount detection circuit 108 detects apeak signal from the signals of the line sensor. The accumulation stopdetermination circuit 109 compares the peak signal with an accumulationstop level (predetermined threshold value) to perform an accumulationstop determination of charges. The ON/OFF control of the transfertransistor MTX is performed in synchronization with the line selectionswitch LSEL. In other words, the control signal φTXn and the line signalφLSn are output synchronously with each other. When the line selectionswitch LSEL is controlled to be switched from a certain line sensor toanother line sensor, a non-selection time period ΔTs (predetermined timeperiod) is provided between ON time periods of each line selectionsignal. The non-selection time period ΔTs has an effect of reducingpower consumed by the AF sensor 101 by turning off the current sources 1and 2 of the signal buffer amplifier and also by turning off the powerof the accumulation stop determination circuit 109. After the time t3,the same operation similar to that during the time period from times t2to t3 is repeated to perform the accumulation stop determination of theline sensor.

Time t4 is a time period for the accumulation stop determination. Inthis embodiment, it is assumed that the accumulation stop determinationis performed at time t4. When the peak signal of the line sensor 102 islarger than an accumulation stop level, the accumulation stopdetermination circuit 109 performs the accumulation stop determination(i.e., determines to stop the accumulation of charges). In this case,the controller 106 turns off the switch SWCH of the line sensor 102 tostore the voltage signal in the memory capacity Cs.

During a time period from times t5 to t6, the line selection switchesLSEL are turned on in sequence according to the line selection signalsφLSn, and the accumulation stop determination circuit 109 performs theaccumulation stop determination. However, the line sensor 102 hasalready stopped the accumulation of charges. Accordingly, the lineselection switches LSEL of the remaining line sensors 103 to 105 areturned on in sequence, and the accumulation stop determination circuit109 performs the accumulation stop determination. The ON/OFF drive ofthe transfer transistor MTX is performed in synchronization with theline selection switch LSEL. After the time t6, each of the lineselection and the accumulation stop determination is repeated until theaccumulation stop determination is performed for all the line sensors.However, the line selection for a line sensor where it is determinedthat the accumulation is to be stopped is skipped.

As described above, in the charge accumulation operation of the secondaccumulation mode in this embodiment, the line selection switch LSEL isturned on during the charge accumulation, and the transistor MTX isturned off in synchronization with the timing of performing theaccumulation stop determination to perform the accumulation stopdetermination. With respect to the line for which it is determined thatthe accumulation is to be stopped during the charge accumulation, theoperation of the accumulation stop determination is skipped, and thus aline selection period is switched and also the line selection period andan ON/OFF period of the transfer transistor MTX are synchronized witheach other.

Next, referring to FIG. 10, a reason for turning off the transfertransistor MTX in synchronization with the timing of performing theaccumulation stop determination with the line selection switch LSELturned on will be described. FIG. 10 is a schematic diagram of apotential of the AF sensor 101 and generated charges in this embodiment.FIG. 10 illustrates a case where a state (state in FIG. 8A) in which thetransfer transistor MTX is turned on and the charges accumulated by thephotodiode PD are transferred to the FD region is transited to a statein which the transfer transistor MTX is turned off.

By turning off the transfer transistor MTX, the charges under the gateof the transfer transistor MTX are moved to the FD region. The transfertransistor MTX is controlled to be in an OFF state from the stateillustrated in FIG. 8A to the time period of the accumulation stopdetermination only while the accumulation stop determination circuit 109performs the accumulation stop determination, and thus a transferfailure of charges such as a deterioration of linearity is avoided andthe dynamic range can be widened. However, if the number of repetitionsof ON/OFF of the transfer transistor MTX increases, there is apossibility that an S/N ratio (signal-to-noise ratio) is deteriorated.Accordingly, in the focus detection operation of this embodiment, it ispreferred that the ON/OFF period of the transfer transistor MTX isswitched (changed) depending on a situation of an object.

Next, referring to FIG. 11, the focus detection operation of the imagepickup apparatus 10 in this embodiment will be described. FIG. 11 is aflowchart of illustrating the focus detection operation in thisembodiment. Each step in FIG. 11 is performed based on an instruction ofthe CPU 100 or the controller 106 of the AF sensor 101. FIG. 11 is aflowchart of illustrating the focus detection operation in the secondaccumulation mode of the two accumulation modes of the AF sensor 101(i.e., the first accumulation mode and the second accumulation modedescribed above).

First, at step S1200, the CPU 100 performs a communication (accumulationstart communication) with the AF sensor 101 to start a chargeaccumulation. According to this communication, the controller 106 setsan accumulation mode to the second accumulation mode. Furthermore, thecontroller 106 sets the non-selection time period ΔTs of the line sensordescribed referring to FIG. 7 to a relatively short time period Ta(ΔTs=Ta). The AF sensor 101 starts the accumulation of charges afterperforming a reset operation. Then, the controller 106 controls theaccumulation stop determination circuit 109 so that the accumulationstop determination for the line sensors 102 to 105 is performed with arelatively short time period.

Subsequently, at step S1201, a counter (not illustrated) provided in theCPU 100 is reset once, and then the counter starts. This counter is usedto measure an accumulation time in the AF sensor 101. Subsequently, atstep S1202, the CPU 100 determines whether the accumulation time in theAF sensor 101 reaches a maximum accumulation time Tmax. The maximumaccumulation time Tmax is a maximum value of a permissible accumulationtime, and it is set and stored in the CPU 100 in advance. If a currentcounter value of the counter provided in the CPU 100 does not reach themaximum accumulation time Tmax, the flow proceeds to step S1204. On theother hand, if the current counter value reaches the maximumaccumulation time Tmax, the flow proceeds to step S1203.

At step S1203, the CPU 100 performs a communication (accumulation endcommunication or accumulation stop communication) with the AF sensor 101to terminate the accumulation of the charges. This communication isperformed by the CPU 100 to terminate the accumulation operationforcibly if the accumulation operation of the AF sensor 101 is notcompleted by the maximum accumulation time Tmax during a photography ina dark situation or the like. When the CPU 100 performs the accumulationstop communication at step S1203, the flow proceeds to step S1210.

At step S1204, the CPU 100 determines whether the charge accumulation inall the line sensors 102 to 105 of the AF sensor 101 are stopped. The AFsensor 101 previously sends information relating to the line sensor inwhich the charge accumulation is terminated. The CPU 100 performs thedetermination based on the information sent from the AF sensor 101. Ifthe charge accumulation in all the line sensors 102 to 105 is stopped,the flow proceeds to step S1210. On the other hand, if any line sensorduring the charge accumulation exists, the flow proceeds to step S1205.

At step S1205, the CPU 100 determines whether the non-selection timeperiod ΔTs of the line sensor is changed from the time period Ta set atstep S1200. If the non-selection time period ΔTs is not changed, theflow proceeds to step S1206. On the other hand, if the non-selectiontime period ΔTs is changed, the flow returns to step S1202.

At step S1206, the CPU 100 determines whether the accumulation time inthe AF sensor 101 reaches a time Th (predetermined time). If the currentaccumulation time reaches the time Th, there is a relatively dark objectand accordingly the flow proceeds to step S1207. On the other hand, thecurrent accumulation time does not reach the time Th, the flow returnsto step S1202. The time Th is set to be shorter than the maximumaccumulation time Tmax (Th<Tmax).

At step S1207, the CPU 100 performs a luminance determination of anobject based on a signal output from the AF sensor 101. Specifically,the CPU 100 communicates with the AF sensor 101, and it requests thepeak signal of the line sensor during the charge accumulation. Then, theCPU 100 acquires object luminance information (object luminance value E)based on a highest signal in the peak signals of the respective linesensors.

Subsequently, at step S1208, the CPU 100 performs the luminancedetermination based on the object luminance information (objectluminance value E) acquired at step S1207. If the object luminanceinformation (object luminance value E) is brighter (larger) than adetermination value (predetermined luminance value Eh) (E≧Eh), the flowreturns to step S1202. On the other hand, if the object luminance valueE is darker (smaller) than the predetermined luminance value Eh (E<Eh),the flow proceeds to step S1209.

At step S1209, the CPU 100 communicates with the AF sensor 101 to resetthe non-selection time period ΔTs. In this embodiment, the CPU 100changes the non-selection time period ΔTs from the time period Ta to atime period Tb (Tb>Ta) that is longer than the time period Ta. As aresult of this communication (i.e., according to the change of thenon-selection time period ΔTs), a period of the accumulation stopdetermination of the line sensor in the AF sensor 101 increases.

At step S1210, the CPU 100 communicates with the AF sensor 101 torequest a pixel signal (signal readout) of each line sensor. Then, theCPU 100 performs A/D conversion of the signals (pixel signals) read fromthe AF sensor 101 in sequence, and it stores the converted signals(digital signals) in a RAM (not illustrated). Subsequently, at stepS1211, the CPU 100 calculates (determines) a defocus amount based on thesignal (pixel signal) of the line sensor acquired at step S1210.Preferably, the CPU 100 selects, from among calculation results of thedefocus amounts calculated based on the signals of the plurality of linesensors, a result with a highest reliability or a result in which adistance from the image pickup apparatus 10 is closest. Subsequently, atstep S1212, the CPU 100 drives the imaging lens 300 via the lenscommunication circuit 205 (lens drive unit) to obtain an appropriatefocus state based on the defocus amount determined at step S1211. Then,a series of focus detection operation is terminated.

As described above, when the object luminance is dark, the non-selectiontime period ΔTs of the line sensor is set to be long so as to increase aperiod of the accumulation stop determination for the line sensors 102to 105. The accumulation time of the line sensor becomes long and thenumber of times of the accumulation stop determination increases if theobject is dark, but according to this embodiment, the number ofrepetitions of ON/OFF of the transfer transistor MTX can be reduced byincreasing the period of the accumulation stop determination. When theobject is dark, the number of generated charges is intrinsically smalland thus a transfer efficiency is easily affected. Accordingly, it ispossible to improve the transfer efficiency by increasing an ON-timeperiod of the transfer transistor MTX. While the ON/OFF control of thetransfer transistor MTX is performed in this embodiment, but it is notlimited thereto. For example, the gate voltage VTXL may be controlled tobe switched between a low state (first state: FIG. 8A) and a high state(second state: FIG. 8B) while the transfer transistor MTX is kept in theON state. In other words, the potential barrier can be set to be at ahigh level during the accumulation stop determination (time period forthe accumulation stop determination: first time period), and on theother hand, the potential barrier can be set to be at a low level duringa time period (second time period) other than the first time period.

While the CPU 100 acquires the object luminance information based on thesignal output from the AF sensor 101 at step S1207, instead, it mayacquire the object luminance information based on a signal output fromthe AE sensor 207. The object luminance may be determined to be dark ifthe accumulation time of the AF sensor 101 reaches the time Th. Whilethe period of determination is switched as binaries (with two differentlevels) depending on the object luminance information in thisembodiment, the number of luminance determination levels may beincreased such that the period is switched as ternaries (with three ormore different levels).

In this embodiment, the photoelectric converter (AF sensor 101) includesa photoelectric conversion portion (photodiode PD), a transfer portion(transfer transistor MTX), a capacitance portion (integral capacity Cfd,memory capacity Cs), a determination unit (accumulation stopdetermination circuit 109), and a setting unit ST. The photoelectricconversion portion receives light from an object to generate charges.The transfer portion transfers the charges generated by thephotoelectric conversion portion. The capacitance portion accumulatesthe charges transferred from the transfer portion. The determinationunit determines whether an accumulation of the charges in thecapacitance portion is to be stopped based on a signal corresponding toa charge amount accumulated in the capacitance portion during a firsttime period (time period for an accumulation stop determination). Thesetting unit sets a height of a potential barrier in the transferportion (transfer channel region). Furthermore, the setting unit changesthe height of the potential barrier in the transfer portion between thefirst time period and a second time period different from the first timeperiod.

Preferably, the determination unit compares the signal corresponding tothe charge amount accumulated in the capacitance portion with areference value (accumulation stop level) to determine whether theaccumulation of the charges in the capacitance portion is to be stopped.For example, this signal is a maximum signal (peak signal) of imagesignals from a corresponding line sensor or a signal relating to afeature amount such as a contrast based on the image signals, but it isnot limited thereto.

Preferably, the setting unit selectively sets a first state in which theheight of the potential barrier is a first height (PB1) and a secondstate in which the height of the potential barrier is a second height(PB2) higher than the first height. In the second state, thedetermination unit determines whether the accumulation of the charges inthe capacitance portion is to be stopped. Preferably, the setting unitsets the transfer portion to the second state during the first timeperiod, and it sets the transfer portion to the first state during thesecond time period. Preferably, the transfer portion transfers thecharges generated by the photoelectric conversion portion to thecapacitance portion in the first state, and it stops transferring thecharges to the capacitance portion in the second state.

Preferably, the photoelectric converter includes a control unit(controller 106) that controls the transfer portion and thedetermination unit synchronously. The control unit controls the transferportion with a first period to repeat the first state and the secondstate. Furthermore, the control unit controls the determination unitwith the first period to determine whether the accumulation of thecharges in the capacitance portion is to be stopped. More preferably,the control unit is capable of changing a synchronous control period ofthe transfer portion and the determination unit depending on objectluminance information. More preferably, the control unit acquires, asthe object luminance information, an object luminance value based on thecharges generated by the photoelectric conversion portion. Then, thecontrol unit maintains the synchronous control period to be in the firstperiod when the object luminance value E is larger than a predeterminedthreshold value (predetermined luminance value Eh). On the other hand,the control unit changes the synchronous control period from the firstperiod to a second period longer than the first period when the objectluminance value is smaller than the predetermined threshold value. Morepreferably, the control unit controls the determination unit so as todetermine, with the first period from an accumulation start of thecharges to a predetermined time, whether the accumulation of the chargesin the capacitance portion is to be stopped. The control unit controlsthe determination unit so as to determine, with a second period longerthan the first period after a passage of the predetermined time, whetherthe accumulation of the charges in the capacitance portion is to bestopped.

Preferably, the photoelectric conversion portion includes a plurality ofphotodiodes. The capacitance portion includes a plurality ofcapacitances corresponding to the plurality of photodiodes,respectively. The control unit controls the determination unit so as to,in sequence, determine whether the accumulation of the charges in eachof the plurality of capacitances is to be stopped. Furthermore, thecontrol unit controls the determination unit so as not to determine,with respect to the capacitance in which the accumulation of the chargesare stopped, whether the accumulation of the charges is to be stopped.Preferably, the control unit stops a power supply to the determinationunit while the transfer unit is in the first state.

Preferably, the control unit includes a first mode (first accumulationmode) and a second mode (second accumulation mode). In the first mode,the control unit transfers the charges generated by the photoelectricconversion portion to the capacitance portion after completion of acharge accumulation period without transferring the charges to thecapacitance portion until the completion of the charge accumulationperiod. In the second mode, the control unit transfers the chargesgenerated by the photoelectric conversion portion to the capacitanceportion during the charge accumulation period and monitor the chargeamount in the capacitance portion. The control unit, in the second mode,controls the transfer portion and the determination unit synchronously.

According to this embodiment, a photoelectric converter, a focusdetection apparatus, and an optical apparatus which improve linearitywith a high dynamic range can be provided.

Second Embodiment

Next, an image pickup apparatus (optical apparatus) in a secondembodiment of the present invention will be described. The AF sensor 101of this embodiment, similarly to the first embodiment, has the firstaccumulation mode (first mode) and the second accumulation mode (secondmode). The AF sensor 101 of this embodiment improves the linearity evenwhen used with a high dynamic range in the second accumulation mode byadopting a configuration different from that in the first embodiment.Other configurations of the image pickup apparatus in this embodimentare the same as those of the image pickup apparatus 10 in the firstembodiment, and accordingly descriptions thereof are omitted.

During the charge accumulation operation in the second accumulationmode, the accumulation stop determination circuit 109 performs theaccumulation stop determination of charges while the transfer transistorMTX is set to be in the ON state during the charge accumulation. Theline sensor for which it is determined that the accumulation is to bestopped stores a voltage signal after the transfer transistor MTX isturned off. By turning off the transfer transistor MTX, the chargesgetting into under the gate of the transfer transistor MTX are moved tothe FD region when the line sensor stores the signal. Accordingly, anappropriate signal with improved linearity can be obtained. On the otherhand, during the charge accumulation, there is a possibility that anerror occurs in the accumulation stop determination of charges due to aninfluence of the charges located under the gate of the transfertransistor MTX.

FIG. 13 is a diagram of illustrating a change of an FD potential (outputvoltage) according to ON/OFF of the transfer transistor MTX. Until theFD potential reaches a potential S3 (between potentials of 0 and S3), anFD potential in a state where the transfer transistor MTX is in the ONstate and an FD potential in a state where the transfer transistor MTXis in the OFF state indicate the same potential as each other, and thusthe FD potential does not vary. On the other hand, when the FD potentialexceeds the potential S3, the charges gets into under the gate of thetransfer transistor MTX, and the FD potential changes depending onON/OFF of the transfer transistor MTX. In other words, as illustrated inFIG. 13, when compared on condition that the accumulation times are thesame each other, the FD potential (second signal, for example apotential S4′) in a state where the transfer transistor is in the ONstate is lower than the FD potential (first signal, for example apotential S4) in a state where the transfer transistor MTX is in the OFFstate.

In this embodiment, the accumulation stop determination circuit 109 orthe controller 106 previously stores a change amount of the FD potential(i.e., information relating to a difference between the first signal andthe second signal). Then, the accumulation stop determination circuit109 sets, as an accumulation stop level (reference value), an FDpotential (potential S4′ as the second signal) corresponding to an FDpotential (potential S4 as the first signal) at which the accumulationis intrinsically to be stopped. In this embodiment, the potential S4 isa saturation level, and the saturation level is determined depending ona dynamic range (D range) of the output circuit 111 of an amplificationcircuit. With respect to the FD potential at which the transfertransistor MTX is in the ON state and the FD potential at which thetransfer transistor MTX is in the OFF state, it is preferred that theaccumulation stop level is previously adjusted to be stored for each AFsensor 101 in a factory or the like. As a result, even if there is avariation of the change amount of the AF sensor 101 individually, it ispossible to perform appropriate control. In this embodiment, this changeamount (i.e., information relating to the difference between the firstsignal and the second signal) is information relating to a change of thetransfer transistor MTX in the respective states, and it may be otherinformation relating to a change such as a change rate.

Next, referring to FIG. 12, an adjustment operation of the accumulationstop level will be described. FIG. 12 is a flowchart of illustrating theadjustment operation of the accumulation stop level. Each step in FIG.12 is performed for example by the CPU 100 for each AF sensor 101.

First, at step S700, the CPU 100 sets a lowest value of zero as aninitial value of an accumulation stop level SLVL set in the AF sensor101. Subsequently, at step S701, the CPU 100 performs an accumulationstart communication with the AF sensor 101. According to thisaccumulation start communication, the CPU 100 sets the accumulation modeto the second accumulation mode, and also it sets the accumulation stoplevel determined at step S700 or S705 to the AF sensor 101.

Subsequently, at step S702, the CPU 100 determines whether theaccumulation of charges in all the line sensors 102 to 105 of the AFsensor 101 is stopped. The AF sensor 101 previously sends, to the CPU100, information relating to the line sensor in which the accumulationof charges is terminated. Accordingly, the CPU 100 performs thedetermination based on the information. If the accumulation in all theline sensors is stopped, the flow proceeds to step S703. On the otherhand, if any line sensor during the charge accumulation remains, the CPU100 continues the accumulation stop determination.

Subsequently, at step S703, the CPU 100 communicates with the AF sensor101 to request an output of a pixel signal of each line sensor. Then,the CPU 100 performs A/D conversion of the pixel signals output (read)from the AF sensor 101 in sequence, and it stores the converted signalsin a RAM (not illustrated). Then, the CPU 100 detects a pixel signalwith a maximum output (maximum value of the pixel signals, i.e., maximumpixel signal) from among the pixel signals of the plurality of linesensors.

Subsequently, at step S704, the CPU 100 compares the maximum value ofthe pixel signals detected at step S703 with the reference value(saturation level S4). If the maximum value of the pixel signals islarger than or equal to the saturation level S4, the flow proceeds tostep S706. On the other hand, if the maximum value of the pixel signalsdoes not reach the saturation level S4, the flow proceeds to step S705.At step S705, the CPU 100 counts up the accumulation stop level SLVL,and it increments the accumulation stop level by one which is to be usedin the subsequent accumulation operation. At step S706, the CPU 100stores the currently set accumulation stop level SLVL in a non-volatilememory (memory 1061), and then it terminates the adjustment operation ofthe accumulation stop level.

Next, referring to FIG. 14, a focus detection operation by the imagepickup apparatus 10 in this embodiment will be described. FIG. 14 is aflowchart of illustrating the focus detection operation in thisembodiment. Each step in FIG. 14 is performed based on an instruction ofthe CPU 100 or the controller 106 of the AF sensor 101. FIG. 14 is aflowchart of illustrating the focus detection operation in the secondaccumulation mode of the two accumulation modes (the first accumulationmode and the second accumulation mode) of the AF sensor 101.

First, at step S1100, the CPU 100 performs a communication (accumulationstart communication) with the AF sensor 101 to start the chargeaccumulation. According to this communication, the controller 106 of theAF sensor 101 sets the accumulation mode to the second accumulationmode. Furthermore, the controller 106 sets, as the accumulation stoplevel SLVL, the accumulation stop level stored by the adjustmentoperation of the accumulation stop level described referring to FIG. 12.

Subsequently, at step S1101, the CPU 100 resets a counter (notillustrated) in the CPU 100 once, and then it starts the counter. Thiscounter is used to measure the accumulation time in the AF sensor 101.Subsequently, at step S1102, the CPU 100 determines whether theaccumulation time in the AF sensor 101 reaches the maximum accumulationtime Tmax. The maximum accumulation time Tmax is a maximum value of apermissible accumulation time, and it is previously set and stored inthe CPU 100. If the current counter value does not reach the maximumaccumulation time Tmax, the flow proceeds to step S1103. On the otherhand, if the current counter value reaches the maximum accumulation timeTmax, the flow proceeds to step S1104.

At step S1103, the CPU 100 performs a communication (accumulation endcommunication or accumulation stop communication) with the AF sensor 101to terminate the accumulation of charges. This communication isperformed by the CPU 100 to terminate the accumulation operationforcibly if the accumulation operation of the AF sensor 101 is notcompleted by the maximum accumulation time Tmax during a photography ina dark situation or the like. When the CPU 100 performs the accumulationstop communication at step S1103, the flow proceeds to step S1105.

At step S1104, the CPU 100 determines whether the charge accumulation inall the line sensors 102 to 105 of the AF sensor 101 is stopped. The AFsensor 101 previously sends, to the CPU 100, the information relating tothe line sensor in which the charge accumulation is terminated. The CPU100 performs the determination based on the information sent from the AFsensor 101. If the charge accumulation in all the line sensors 102 to105 is stopped, the flow proceeds to step S1105. On the other hand, ifthere is any line sensor during the charge accumulation, the flowreturns to step S1102, and the accumulation operation of chargescontinues.

At step S1105, the CPU 100 communicates with the AF sensor 101 torequest a pixel signal (signal readout) of each line sensor. Then, theCPU 100 performs A/D conversion of the signals (pixel signals) read fromthe AF sensor 101 in sequence, and it stores the converted signals(digital signals) in a RAM (not illustrated). Subsequently, at stepS1106, the CPU 100 calculates (determines) a defocus amount based on thesignal (pixel signal) of the line sensor acquired at step S1105.Preferably, the CPU 100 selects, from among calculation results of thedefocus amounts calculated based on the signals of the plurality of linesensors, a result with a highest reliability or a result in which adistance from the image pickup apparatus 10 is closest. Subsequently, atstep S1107, the CPU 100 drives the imaging lens 300 via the lenscommunication circuit 205 (lens drive unit) to obtain an appropriatefocus state based on the defocus amount determined at step S1106. Then,a series of focus detection operation is terminated.

As described above, the AF sensor 101 can be appropriately controlled bypreviously adjusting and setting the accumulation stop levelcorresponding to the change (signal variation) of the FD potentialdepending on ON/OFF (or a height of the potential barrier) of thetransfer transistor MTX. The change of the AF potential depending ON/OFFof the transfer transistor MTX may be different in each pixel of theline sensor. In this case, as illustrated in FIG. 15, the CPU 100 maypreviously store, as a correction value, the change of the pixel signaldepending on ON/OFF of the transfer transistor MTX in an adjustmentstep. FIG. 15 is a diagram of illustrating a relationship of the pixelsignal of the transfer transistor MTX between the ON state and the OFFstate, and a horizontal axis indicates a signal obtained while thetransfer transistor MTX is in the ON state and a vertical axis indicatesa signal obtained while the transfer transistor MTX is in the OFF state.Then, the CPU 100 corrects a pixel signal obtained while the transfertransistor MTX is in the OFF state by using a pixel signal obtainedwhile the transfer transistor MTX is in the ON state during the chargeaccumulation and the stored correction value. Accordingly, the CPU 100,instead of the AF sensor 101, can perform the stop determinationoperation.

As described above, a photoelectric converter (AF sensor 101) includes aphotoelectric conversion portion (photodiode PD), a transfer portion(transfer transistor MTX), a capacitance portion (integral capacity Cfdand memory capacity Cs), and a determination unit (accumulation startdetermination circuit 109). The photoelectric conversion portionreceives light from an object to generate charges. The transfer portiontransfers the charges generated by the photoelectric conversion portion.The capacitance portion accumulates the charges transferred from thetransfer portion. The determination unit determines, based on adetection signal (potential of the detection signal) that corresponds toa charge amount accumulated in the capacitance portion and that isobtained while the transfer portion transfers the charges, whether anaccumulation of the charges in the capacitance portion is to be stopped.In this determination, the determination unit uses information relatingto a difference between a first signal and a second signal. The firstsignal is a signal (for example, a potential S4 as a saturation level)corresponding to the accumulation amount accumulated in the capacitanceportion while the transfer portion stops transferring the charges (in anOFF state). The second signal is a signal (for example, a potential S4′)corresponding to the charge amount accumulated in the capacitanceportion while the transfer portion transfers the charges (in an ONstate). The information relating to the difference between the firstsignal and the second signal is a change amount of the FD potentialaccording to ON/OFF of the transfer portion, but it is not limitedthereto. While this embodiment performs the ON/OFF control of thetransfer transistor MTX, it is not limited thereto. For example, thevoltage VTXL may be controlled to be switched between a low level (firststate in FIG. 8A) and a high level (second state in FIG. 8B) while thetransfer transistor MTX is maintained to be in the ON state.

Preferably, the photoelectric converter includes a memory unit (memory1061) that stores the information relating to the difference between thefirst signal and the second signal. The determination unit determines,based on the detection signal and the information stored in the memoryunit, whether the accumulation of the charges in the capacitance portionis to be stopped.

Preferably, the determination unit compares the detection signal with areference value to determine whether the accumulation of the charges inthe capacitance portion is to be stopped. The reference value is thesecond signal (potential S4′) that is obtained while the transferportion transfers the charges and that is set so that the first signal(potential S4) is obtained while the transfer portion stops transferringthe charges, i.e., the reference value is the second signalcorresponding to the first signal. Preferably, the reference value is avoltage value adjustable depending on a signal variation caused by aheight of a potential barrier in the transfer portion. Preferably, thereference value is a voltage value adjustable for each photoelectricconversion portion.

According to this embodiment, a photoelectric converter, a focusdetection apparatus, and an optical apparatus which improve linearitywith a high dynamic range can be provided.

Third Embodiment

Next, an image pickup apparatus (optical apparatus) in a thirdembodiment of the present invention will be described. The AF sensor 101of this embodiment, similarly to the first embodiment, has the firstaccumulation mode (first mode) and the second accumulation mode (secondmode). The AF sensor 101 of this embodiment improves the linearity evenwhen used with a high dynamic range in the second accumulation mode byadopting a configuration different from that in each of the first andsecond embodiments. Other configurations of the image pickup apparatusin this embodiment are the same as those of the image pickup apparatus10 in the first embodiment, and accordingly descriptions thereof areomitted.

FIG. 16 is a timing chart of illustrating the charge accumulationoperation in the second accumulation mode in this embodiment. In thisembodiment, a voltage VTXL=VTXL2 as a gate voltage is applied (set) tothe transfer transistor MTX while the transfer transistor MTX is in theON state.

In FIG. 16, a time period from times t0 to t1 is a pixel reset timeperiod. When the communication for starting the accumulation is sentfrom the CPU 100, the controller 106 of the AF sensor 101 turns on theswitch SWRES and the transfer transistor MTX to reset each of potentialsof the photodiode PD and the integral capacity Cfd to the voltage VRESaccording to the control signals φRES and φTXn. The transfer transistorMTX keeps the ON state after the time t1, and accordingly the chargesgenerated by the photodiode PD are accumulated in the integral capacityCfd.

During a time period from times t2 to t3, the charges generated by thephotodiode PD are accumulated in the integral capacity Cfd since thetransfer transistor MTX is in the ON state. On the other hand, the lineselection switches LSEL of the line sensor 102 to 105 are turned on insequence according to line selection signals φLSn. Signals of the linesensor selected by the line selection switch LSEL are output to thesignal amount detection circuit 108. Then, the signal amount detectioncircuit 108 detects a peak signal from the signals of the line sensor.The accumulation stop determination circuit 109 compares the peak signalwith an accumulation stop level (predetermined threshold value) toperform an accumulation stop determination of charges. When the lineselection switch LSEL is controlled to be switched from a certain linesensor to another line sensor, a non-selection time period ΔTs(predetermined time period) is provided between ON time periods of eachline selection signal. The non-selection time period ΔTs has an effectof reducing power consumed by the AF sensor 101 by turning off thecurrent sources 1 and 2 of the signal buffer amplifier and also byturning off the power of the accumulation stop determination circuit109.

During this time period, the transfer transistor MTX is in the ON stateand the voltage VTXL=VTXL2 are a gate voltage is applied to the transfertransistor MTX. Accordingly, the potential is in the state (secondstate) illustrated in FIG. 8B, and a linearity failure occurs due to theinfluence of the transfer time as described above (in the firstembodiment). However, a time period from an accumulation start time ofcharges (time 1) to a predetermined time (time t3) is a sufficientlyshort time period, and an object for which the accumulation stopdetermination is to be performed during this time period is in asufficiently bright state. Accordingly, the influence of the transfertime is minor, and a signal linearity can be sufficiently ensured.Conversely, the time t3 may be determined based on a luminance in whichthe linearity can be ensured.

During a time period from times t3 to t4, the transfer transistor MTX isin the OFF state, and accordingly the charges generated by thephotodiode PD are accumulated in the photodiode PD.

During a time period after a time t4, the transfer transistor MTXperforms ON/OFF control in synchronization with the line selectionswitch LSEL. The line selection switches LSEL of the line sensor 102 to105 are turned on in sequence according to line selection signals φLSn.Furthermore, a non-selection time period ΔTs (predetermined time period)is reset to increase. This embodiment is different from the firstembodiment in that the control signal φTXn is turned on prior to theline selection signal φLSn by ΔTtr. By turning on the control signalφTXn prior to the line selection signal φLSn by ΔTtr, the transfer timein which the charges accumulated by the photodiode PD can be completelytransferred to the integral capacity Cfd before the line selection andthe accumulation stop determination are ensured. Similarly, an intervalof the line selection (non-selection time period ΔTs) is set toincrease.

While detail descriptions are omitted, the accumulation stop operationis performed similarly to the first embodiment and the line sensor forwhich the accumulation is stopped is controlled so as not to be selectedif it is determined that the accumulation is to be stopped during theline selection operation after the time t2.

In this embodiment, the photoelectric converter (AF sensor 101) includesa photoelectric conversion portion (photodiode PD), a transfer portion(transfer transistor MTX), a capacitance portion (integral capacity Cfd,memory capacity Cs), a determination unit (accumulation stopdetermination circuit 109), and a setting unit ST. The photoelectricconversion portion receives light from an object to generate charges.The transfer portion transfers the charges generated by thephotoelectric conversion portion. The capacitance portion accumulatesthe charges transferred from the transfer portion. The determinationunit determines whether an accumulation of the charges in thecapacitance portion is to be stopped based on a signal corresponding toa charge amount accumulated in the capacitance portion during a firsttime period (time period for an accumulation stop determination). Thesetting unit sets a height of a potential barrier in the transferportion (transfer channel region). The setting unit maintains the heightof the potential barrier to be constant between the first time periodand the second time period from an accumulation start time (time t1) ofthe charges to a predetermined time (time t3), and changes the height ofthe potential barrier between the first time period and the second timeperiod after a passage of the predetermined time. In this embodiment,with respect to the line selection operation after the time t3 and thecontrol of the transfer transistor MTX, the control method described inthe first embodiment or the second embodiment can also be applied.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

While each embodiment describes, as an optical apparatus, the imagepickup apparatus such as a still camera and a movie camera, it is notlimited thereto and for example it can be applied also to an opticalapparatus, such as a telescope and a projector, which does not have afunction of capturing an image.

This application claims the benefit of Japanese Patent Application No.2015-083056, filed on Apr. 15, 2015, Japanese Patent Application No.2015-115721, filed on Jun. 8, 2015, and Japanese Patent Application No.2016-042970, filed on Mar. 7, 2016, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. A photoelectric converter comprising: aphotoelectric conversion portion configured to receive light from anobject to generate charges; a transfer portion configured to transferthe charges generated by the photoelectric conversion portion; acapacitance portion configured to accumulate the charges transferredfrom the transfer portion; a comparator configured to compare a signalcorresponding to a charge amount accumulated in the capacitance portionduring a first time period with a predetermined threshold value, so asto determine whether an accumulation of the charges in the capacitanceportion is to be stopped; and an output buffer configured to output apredetermined voltage, so as to set a height of a potential barrier inthe transfer portion, wherein the output buffer is configured to changethe predetermined voltage, so as to change the height of the potentialbarrier in the transfer portion between the first time period and asecond time period different from the first time period.
 2. Thephotoelectric converter according to claim 1, wherein the comparator isconfigured to compare the signal corresponding to the charge amount witha reference value to determine whether the accumulation of the chargesin the capacitance portion is to be stopped.
 3. The photoelectricconverter according to claim 1, wherein: the output buffer is configuredto selectively set a first state in which the height of the potentialbarrier is a first height and a second state in which the height of thepotential barrier is a second height higher than the first height, andthe comparator is configured to determine, in the second state, whetherthe accumulation of the charges in the capacitance portion is to bestopped.
 4. The photoelectric converter according to claim 3, whereinthe output buffer is configured to: set the transfer portion to thesecond state during the first time period, and set the transfer portionto the first state during the second time period.
 5. The photoelectricconverter according to claim 3, wherein the transfer portion isconfigured to: transfer the charges generated by the photoelectricconversion portion to the capacitance portion in the first state, andstop transferring the charges to the capacitance portion in the secondstate.
 6. The photoelectric converter according to claim 3, furthercomprising a controller configured to control the transfer portion andthe comparator synchronously, wherein the controller is configured to:control the transfer portion with a first period to repeat the firststate and the second state, and control the comparator with the firstperiod to determine whether the accumulation of the charges in thecapacitance portion is to be stopped.
 7. The photoelectric converteraccording to claim 6, wherein the controller is capable of changing asynchronous control period of the transfer portion and the comparatordepending on object luminance information.
 8. The photoelectricconverter according to claim 7, wherein the controller is configured to:acquire, as the object luminance information, an object luminance valuebased on the charges generated by the photoelectric conversion portion,maintain the synchronous control period to be in the first period whenthe object luminance value is larger than a predetermined thresholdvalue, and change the synchronous control period from the first periodto a second period longer than the first period when the objectluminance value is smaller than the predetermined threshold value. 9.The photoelectric converter according to claim 7, wherein the controlleris configured to: control the comparator so as to determine, with thefirst period from an accumulation start of the charges to apredetermined time, whether the accumulation of the charges in thecapacitance portion is to be stopped, and control the comparator so asto determine, with a second period longer than the first period after apassage of the predetermined time, whether the accumulation of thecharges in the capacitance portion is to be stopped.
 10. Thephotoelectric converter according to claim 6, wherein: the photoelectricconversion portion includes a plurality of photodiodes, the capacitanceportion includes a plurality of capacitances corresponding to theplurality of photodiodes, respectively, and the controller is configuredto: control the comparator so as to, in sequence, determine whether theaccumulation of the charges in each of the plurality of capacitances isto be stopped, and control the comparator so as not to determine, withrespect to the capacitance in which the accumulation of the charges arestopped, whether the accumulation of the charges is to be stopped. 11.The photoelectric converter according to claim 6, wherein the controlleris configured to stop a power supply to the comparator while the heightof the potential barrier in the transfer portion is in the first state.12. The photoelectric converter according to claim 6, wherein thecontroller includes a first mode and a second mode, and the controlleris configured to: in the first mode, transfer the charges generated bythe photoelectric conversion portion to the capacitance portion aftercompletion of a charge accumulation period without transferring thecharges to the capacitance portion until the completion of the chargeaccumulation period, in the second mode, transfer the charges generatedby the photoelectric conversion portion to the capacitance portionduring the charge accumulation period and monitor the charge amount inthe capacitance portion, and in the second mode, control the transferportion and the comparator synchronously.
 13. A photoelectric convertercomprising: a photoelectric conversion portion configured to receivelight from an object to generate charges; a transfer portion configuredto transfer the charges generated by the photoelectric conversionportion; a capacitance portion configured to accumulate the chargestransferred from the transfer portion; and a comparator configured tocompare a detection signal corresponding to a charge amount accumulatedin the capacitance portion with a predetermined threshold value, so asto determine whether an accumulation of the charges in the capacitanceportion is to be stopped, the detection signal being obtained while thetransfer portion transfers the charges, wherein the comparator isconfigured to determine whether the accumulation of the charges in thecapacitance portion is to be stopped, by using information relating to adifference between a first signal corresponding to an accumulationamount accumulated in the capacitance portion while the transfer portionstops transferring the charges and a second signal corresponding to anaccumulation amount accumulated in the capacitance portion while thetransfer portion transfers the charges.
 14. The photoelectric converteraccording to claim 13, further comprising a memory configured to storethe information relating to the difference between the first signal andthe second signal, wherein the comparator is configured to determine,based on the detection signal and the information stored in the memory,whether the accumulation of the charges in the capacitance portion is tobe stopped.
 15. The photoelectric converter according to claim 13,wherein: the comparator is configured to compare the detection signalwith a reference value to determine whether the accumulation of thecharges in the capacitance portion is to be stopped, and the referencevalue is the second signal that is obtained while the transfer portiontransfers the charges and that is set so that the first signal isobtained while the transfer portion stops transferring the charges. 16.The photoelectric converter according to claim 15, wherein the referencevalue is a voltage value adjustable depending on a signal variationcaused by a height of a potential barrier in the transfer portion. 17.The photoelectric converter according to claim 15, wherein the referencevalue is a voltage value adjustable for each photoelectric conversionportion.
 18. The photoelectric converter according to claim 1, whereinthe output buffer is configured to: maintain the height of the potentialbarrier to be constant between the first time period and the second timeperiod from an accumulation start time of the charges to a predeterminedtime, and change the height of the potential barrier between the firsttime period and the second time period after a passage of thepredetermined time.
 19. A focus detection apparatus comprising: aphotoelectric conversion portion configured to receive light from anobject to generate charges; a transfer portion configured to transferthe charges generated by the photoelectric conversion portion; acapacitance portion configured to accumulate the charges transferredfrom the transfer portion; a comparator configured to compare a signalcorresponding to a charge amount accumulated in the capacitance portionduring a first time period with a predetermined threshold value, so asto determine whether an accumulation of the charges in the capacitanceportion is to be stopped; an output buffer configured to output apredetermined voltage, so as to set a height of a potential barrier inthe transfer portion; and a detector configured to detect a defocusamount based on the signal, wherein the output buffer is configured tochange the predetermined voltage, so as to change the height of thepotential barrier in the transfer portion between the first time periodand a second time period different from the first time period.
 20. Afocus detection apparatus comprising: a photoelectric conversion portionconfigured to receive light from an object to generate charges; atransfer portion configured to transfer the charges generated by thephotoelectric conversion portion; a capacitance portion configured toaccumulate the charges transferred from the transfer portion; acomparator configured to compare a detection signal corresponding to acharge amount accumulated in the capacitance portion with apredetermined threshold value, so as to determine whether anaccumulation of the charges in the capacitance portion is to be stopped,the detection signal being obtained while the transfer portion transfersthe charges; and a detector configured to detect a defocus amount basedon the signal, wherein the comparator is configured to determine whetherthe accumulation of the charges in the capacitance portion is to bestopped, by using information relating to a difference between a firstsignal corresponding to an accumulation amount accumulated in thecapacitance portion while the transfer portion stops transferring thecharges and a second signal corresponding to an accumulation amountaccumulated in the capacitance portion while the transfer portiontransfers the charges.
 21. An optical apparatus comprising: aphotoelectric conversion portion configured to receive light from anobject to generate charges; a transfer portion configured to transferthe charges generated by the photoelectric conversion portion; acapacitance portion configured to accumulate the charges transferredfrom the transfer portion; a comparator configured to compare a signalcorresponding to a charge amount accumulated in the capacitance portionduring a first time period with a predetermined threshold value, so asto determine whether an accumulation of the charges in the capacitanceportion is to be stopped; an output buffer configured to output apredetermined voltage to set a height of a potential barrier in thetransfer portion; a detector configured to detect a defocus amount basedon the signal; and a lens driver configured to drive a lens based on thedefocus mount detected by the detection unit, wherein the output bufferis configured to change the predetermined voltage, so as to change theheight of the potential barrier in the transfer portion between thefirst time period and a second time period different from the first timeperiod.
 22. An optical apparatus comprising: a photoelectric conversionportion configured to receive light from an object to generate charges;a transfer portion configured to transfer the charges generated by thephotoelectric conversion portion; a capacitance portion configured toaccumulate the charges transferred from the transfer portion; acomparator configured to compare a detection signal corresponding to acharge amount accumulated in the capacitance portion with apredetermined threshold value, so as to determine whether anaccumulation of the charges in the capacitance portion is to be stopped,the detection signal being obtained while the transfer portion transfersthe charges; a detector configured to detect a defocus amount based onthe signal; and a lens driver configured to drive a lens based on thedefocus mount detected by the detection unit, wherein the comparator isconfigured to determine whether the accumulation of the charges in thecapacitance portion is to be stopped, by using information relating to adifference between a first signal corresponding to an accumulationamount accumulated in the capacitance portion while the transfer portionstops transferring the charges and a second signal corresponding to anaccumulation amount accumulated in the capacitance portion while thetransfer portion transfers the charges.
 23. A method of controlling aphotoelectric converter, the method comprising: receiving, by aphotoelectric conversion portion, light from an object to generatecharges; transferring, by a transfer portion, the charges generated bythe photoelectric conversion portion; accumulating, by a capacitanceportion, the charges transferred from the transfer portion; comparing,by a comparator, a signal corresponding to a charge amount accumulatedin the capacitance portion during a first time period with apredetermined threshold value, so as to determine whether anaccumulation of the charges in the capacitance portion is to be stopped;and outputting, by an output buffer, a predetermined voltage to set aheight of a potential barrier in the transfer portion, wherein theoutput buffer is configured to change the predetermined voltage, so asto change the height of the potential barrier in the transfer portionbetween the first time period and a second time period different fromthe first time period.
 24. A method of controlling a photoelectricconverter, the method comprising: receiving, by a photoelectricconversion portion, light from an object to generate charges;transferring, by a transfer portion, the charges generated by thephotoelectric conversion portion; accumulating, by a capacitanceportion, the charges transferred from the transfer portion; andcomparing, by a comparator, a detection signal corresponding to a chargeamount accumulated in the capacitance portion with a predeterminedthreshold value, so as to determine whether an accumulation of thecharges in the capacitance portion is to be stopped, the detectionsignal being obtained while the transfer portion transfers the charges,wherein the comparator is configured to determine whether theaccumulation of the charges in the capacitance portion is to be stopped,by using information relating to a difference between a first signalcorresponding to an accumulation amount accumulated in the capacitanceportion while the transfer portion stops transferring the charges and asecond signal corresponding to an accumulation amount accumulated in thecapacitance portion while the transfer portion transfers the charges.